Solar Panel Water Heaters, Are They Worth It?

solar hot water heater systems

A solar boiler can help you make significant savings on your energy bill. Whether you use natural gas or electricity to keep your hot water tank hot, a solar boiler can help you boost those savings by up to 85% during the summer and around 35% during the winter. This means that in a year, you can save on average 60% on your hot water bill. 

As water heating is usually the biggest portion of a US energy bill, it is good to know that you can slash this use. A solar boiler uses a solar collector and a hot water tank to supply hot water for residential use to your home. Unlike a conventional water heater, a solar boiler uses free solar energy and very little electricity. 

The only electricity that is used in a solar boiler is the electricity used to run the pump that pulls the water from the solar collectors. The water is then pushed through a heat exchanger, and back to the solar collector. It gets heated in the collector. There is so much energy there that you could even cook with sunlight. With a setup like this, there are very few moving parts and there is minimal maintenance. 

What is a Solar Boiler?

A setup like this, with a collector, heat exchanger, and the water tank is one of the best ways to use solar energy. A solar boiler is a simple device that is installed on your rooftop and that uses solar energy to turn cold water into hot. As everyone’s needs are different, so are the sizes of the storage tank in any setup. 

Every solar boiler is a cost-effective device that features high efficiency. If you choose the right model and the right installer, they will also install all the piping for you and will be able to insulate this piping. This way, the already high efficiency will be even higher, and your solar boiler will be able to provide domestic hot water for a bigger family. 


When choosing the size of the solar boiler, it is important to know that solar water heating is not done on demand. Rather, your boiler will use solar power when it is available – during the day. With this in mind, it is easy to see why a water tank is so necessary – to help offset the difference between the time when there is sunlight available and when the household water is actually used – during early mornings and late nights. 

Although the water tank reduces the efficiency of any solar boiler, as waste heat is radiated, the overall efficiency of collectors and the entire setup will help you save both gas and electricity, especially in climates with a lot of sunlight. Nevertheless, cold climates can also see significant savings, although a bit lower. 

If you would like a simple off-grid solar water heating system, you can go for a small off-shelf system which you can purchase in most specialized stores. However, if you would like a more robust system for both an on-grid or off-grid home, you should talk to an expert or do the calculations for you. Always allow for some wiggle room, as daily and seasonal temperature and insolation changes can influence the efficiency of the whole system. 

In general, you will need to cover around 20 sq. feet for the initial two family members. For every additional family member, you will need to cover an additional 8 sq. feet in solar collectors. This will allow for enough hot water to be produced in your solar energy system. Beware that oversizing the system can reduce its high efficiency and overheat the water – leading to temperatures that can cause injury. 

No. Family MembersSolar Collector Area Needed
240 sq. feet / 4 sq. meter
348 sq. feet / 4.8 sq. meter
456 sq. feet / 5.6 sq. meter
564 sq. feet / 6.4 sq. meter

Once you know the surface you need to cover in solar collectors, you also need to understand how to calculate the size of the storage tank. As every home and every family’s needs are different, you need to do your own calculations. In general, you will need to be able to store as much as 2 gallons of water per 1 sq. foot of collector space. This will allow you to keep enough hot water for your needs. 

When calculating the needs, you should also be able to count in any other appliances that may need to access that hot water, such as a dishwasher or a washer with a hot water inlet. Most of these will add to your hot water consumption and you may need a bigger system and a bigger storage tank to fully utilize the renewable sources on your property. 

When deciding on the size of the system, you should also be able to count on all the other factors that you can observe on your property. These include the orientation and the tilt of your roof, the desired water temperature, as well as the number of sunny hours on a summer day, and the average sunny hours in a year. 

How Does it Work?

Once all the calculations are done, you should know how a solar boiler system works. You should be able to understand how your investment will be paid off to you. The solar collector system works by either providing hot water on its own or by adding energy to the system you already have, such as a natural gas water heater. 

In any case, the heat is provided by the sun and is then immediately stored or sent to a storage system by means of a heat-transfer fluid. The heat-transfer fluid is usually water with some added chemicals which are supposed to prevent the water from freezing in the pipes or the collectors during the winter. 

A system like this can be both active and passive. Both kinds have their advantages and disadvantages. Although an active system may be more efficient, it will also be more prone to breakage and will need electricity to pump the hot water to the storage tank. On the other hand, although passive systems may have low efficiency, they ask for no electricity input, so they only run on renewable sources and are a much better solution in most cases, including off-grid systems. 

Solar Hot Water System

Every solar hot water system has integral parts that are necessary for the system to function. There are the following parts that you, or your contractor, should take into consideration: 

  • The solar collector, which collects (therefore the name) solar energy, 
  • The energy pack, which exchanges the heat, and 
  • The solar storage tank. 

Solar Collector

The solar collector is the first thing that comes to your mind when you think of how to use solar energy to keep the water hot. This is the part that is exposed to sun and sunlight. It is usually dark in color and made of metal or a plastic-type of material. Occasionally, it will be made of a series of vacuum or air-evacuated tubes, which feature higher efficiency, but may not be worth the extra investment. There are three basic types of solar collectors: 

Flat-Plate Collector

A flat-plate collector has a flat, usually glazed surface mounted on the rooftop and a dark absorber plate under the glazing. They are insulated, weatherproof boxes, but occasionally they may come in as a flat foldable panel made of plastic or polymer materials that are used for heating pools. Although much cheaper, they are also much less efficient but may be spread on the ground in the spring or early summer to heat up the fresh pool water. 

Integral Collector-Storage Systems

Integral collector storage systems have a collection tank within an insulated box with a layer of glass or plastic on top. The inner side of the box is painted black, to help absorb as much heat as possible. The storage tank inside the box can sometimes be quite heavy, so you will need a professional to install it on the roof, as the bearings need to be examined first, to ensure that the structure is not compromised. 

Evacuated-Tube Solar Collectors

An evacuated-tube solar collector is a state-of-art device that heats the water. The evacuated tubes are cylindrical in shape and can catch sunlight from almost all angles. This makes the collector system more reliable, as you will be getting some hot water even in the early morning hours, and sometimes, even if the sky is slightly overcast. This makes them the perfect renewable energy system. On top of a system like this comes an insulated storage tank, so the added weight may not be the best solution for all. 

Energy Pack

The energy pack is an integral part of active boilers. An energy pack is, simply put, the active part of a system like this. It has at least one low-voltage water pump that circulated the heat-bearing fluid through the collector and back to the heat exchanger. The other pump (although some systems are passive in the second phase), circulates the heated water to the storage tank and back. An energy pack allows for higher efficiency and more heated water as a result but may cost more. This system may be more reliable, and for a longer period of the day, but more moving parts increase the chances of breakage and higher maintenance costs. 

Solar Storage Tank

The solar storage tank can be any hot water tank. The basic idea is that the heat-exchanging element can be mounted inside or that the tank has enough inlets and outlets to allow for a water pump to be installed. If you are purchasing an entire system on your own, always purchase kits, as they’ve been designed to work well together. 

You also need to pay special attention to the size of the storage tank, to make sure that the size is enough for your family. If you have a hot tub, for example, you will need a bigger solar storage tank. If finances or space are a limiting factor, you should consider purchasing a smaller unit that can also use another type of fuel, to help the system out during cloudy days or during winter. 

Types of Solar Water Heating Systems

As there are many different systems, there are also different types of solar heaters. The basic types can be active and passive. The active systems include direct circulation systems and indirect circulation systems. Passive systems include integral collector-storage passive systems and thermosyphon systems. Let’s consider them in more detail. 

Active Solar Water Heating Systems

Active solar heating systems for domestic water use are considered to be of higher efficiency when compared to passive solar systems. However, they:

  • Have more moving parts, 
  • Are prone to breakage, 
  • Cost more than passive systems, 
  • Are bigger systems that require more space, and 
  • Take longer to pay off. 

In addition to this, active systems cannot be mounted or dismounted as easily and may not be as mobile, which makes them impractical in RV and other portable applications. 

Direct Circulation Systems

Direct circulation systems circulate domestic water directly. They are cheaper than indirect systems, have fewer parts, and are likely to be used in climates where freezing temperatures happen occasionally. They are usually not used to freezing climates, as there is a high chance of pipes bursting and resulting in damage. 

Indirect Circulation Systems.

Indirect circulation systems, also called indirect recirculation systems, circulate freeze-resistant liquid or water with antifreeze properties through the collectors. They then circulate this liquid through a heat exchanger. With a setup like this, you can have hot water even in climates prone to freezing. 

Passive Solar Water Heating Systems

Passive systems, on the other hand, feature lower efficiency, but have more uses and are less prone to breakage, as there are no pumps. All passive systems use zero external energy and have no moving parts. They are also more reliable and better suited to temporary residences since there is less maintenance and they are easy to completely void of water when you leave the residence for a while. 

Integral Collector-Storage Passive Systems

Internal collector-storage passive systems consist of an insulated box that has an absorber plate inside and the storage unit as well. These systems use water pressure from the house piping itself, have no moving parts, and have very little need for maintenance. The thing to look out for is mineral deposits if you live in an area with “hard” water. These systems are very inexpensive. 

Thermosyphon Systems

Thermosyphon systems contain a considerable length of pipes that the water flows through when a hot water faucet is opened. Most of these have a significant water holding capacity of around 40 gallons, which is more than enough for a shower and domestic use. The biggest benefit of these systems is that cold water is reheated as soon as it enters the system. 

Installation & Maintenance

Installation and maintenance of solar energy boilers are highly recommended to be done by the same company. This way, you are sure that you have a functional system that will decrease your carbon footprint and your reliance on oil. You will also have a lower electricity need and you can even install a smaller solar panel system if going carbon-neutral is what you prefer. 

It is always best to let professionals install your system. This is especially true if you are retrofitting an older system. Any piece of a pipe that is not insulated well enough and any valve that may leak can significantly reduce the efficiency of your system. For this reason, hiring professionals and paying a bit extra can help you save even more over the upcoming decades. 

When it comes to the maintenance of solar boilers, it is very easy and, in most cases, it can be done every few years. Cleaning the glazing on top of the collector, as well as removing mineral deposits in direct circulation systems is necessary, especially in areas with little rainfall, a lot of dust, and hard water. 

In any case, both the maintenance and the installation should always be done by certified, experienced professionals. This way, you are sure that your equipment is still covered by warranty and that no leaks will compromise the security of your home. This way, you can also have peace of mind that your system will provide enough hot water for your needs. 

Factors to Consider Before Buying a Solar Water Heater

solar water heating system for home

Of course, before making your purchase, you should consider several factors. These are the things to take into consideration before choosing the best solar heater for your home: 

  • The size of your home, 
  • The purpose of the solar boiler – having domestic hot water and heating your home using solar energy are two different things, 
  • The size of your family – the more the merrier, but a bigger family will need a bigger boiler, 
  • Your energy needs – showering twice a day instead of once will double your energy consumption and will result in double the size of your solar collector, 
  • The energy efficiency level of your home – the lower the efficiency, the more energy your home will use and the more hot water it will need, 
  • The funds available – as bigger, more efficient, active systems cost more money, but may be more efficient to the point that they pay off faster, 
  • The availability of solar incentives in your area. 

Energy Saving Tips for Solar Boilers

Having a solar boiler is a great improvement and investment in your home. However, not all solar boiler owners see the same results. The secret is: how you use hot water around your home. As no two homes are the same, we will outline the basic tips on how to save energy with a solar boiler: 

  • Make sure that all hot water piping, both from the collector to the solar hot water tank and from the tank onwards is insulated
  • Check twice a year for any leaks, as they can significantly decrease the efficiency of your hot water collector, 
  • Check if you have a hot water recirculation system – having one will significantly increase your energy consumption, but may not always be needed, 
  • Check if your in-home hot water pipes are insulated – always consider that saving energy is better than having to produce more, 
  • Check if the temperature is set to the right level  having a system that is set to too high of a temperature can mean that the adjunct heating systems have to come on more often than is really needed, 
  • Install a thermal regulator valve – these valves mix hot and cold water to both improve your safety and decrease energy consumption, 
  • Make sure no taps leak water in your home, 
  • Make sure that you switch as many devices as you can to hot water – running your washer and dishwasher on hot water from a system like this will increase your hot water consumption, but will decrease your overall natural gas and electricity consumption, and 
  • Install a heat-recovery brass wastewater pipe in the basement – these pipes are simple to install, cost very little, and can recover around 50% of the heat that is otherwise lost to the sewer lines, 
  • Install a heat pump – and use up to 6 times less energy for heating than before. 

Solar Tax Incentives

You can always use the Federal Solar ITC – Investment Tax Credit. By the end of 2024, you can get a 22% tax credit for any solar water heater installation. You should always check if your state has other solar tax incentives or rebates. Most banks in the US will also give you an interest-free solar loan for bigger projects. 


What Can Go Wrong with a Solar Hot Water System?

The most common problems that you can have with your solar hot water system include sediment build-up in pipes and shading from local vegetation. Sediment build-up is a problem on its own and can occur in any region that has a lot of limescale in its water supply. Vegetation, especially trees, can keep growing even after your solar boiler is installed and cast shade. In thi case, you can simply extend the system or switch its position on the roof. 

Why is my Solar Hot Water Only Warm?

The most common reason why your solar hot water is only warm is that there may not be enough sunlight. Cloudy days and surrounding vegetation can restrict how much sunlight hits your solar collector and can reduce your solar water heating efficiency. A solar collector with plenty of sunlight will always give enough hot water, for as long as your system is large enough. 

Does Solar Hot Water Work in Winter?

Depending on the region you live in, they may. If you get a lot of sunlight during winter time, your solar boiler will produce plenty of hot water. If you live in very cold, cloudy areas, they may not be able to do so. In most regions, November-February/March hot water production is too low for a household and you may even need to use an additional boiler unit. 

Can a Solar Water Heater Overheat?

Yes, a solar water heater can overheat. All the hot water that is produced has to go somewhere or it will overheat your system. There are ways to combat this, such as opening a hot water tap for a few minutes during the hottest part of the day. In any case, there is no place to worry, as most solar hot water boilers have security valves that can protect themselves from malfunctioning. 


Going solar for domestic water use is a sure way to save a lot of energy and reduce your carbon footprint. With a system like this, you can forget about high energy bills for both electricity and natural gas. A solar boiler is a simple system that you can rely on and depend on. It will supply you with hot water with very little maintenance and very little input once it is in place. 

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